The present invention relates to the detection of arcing faults in the stator windings of large dynamoelectric machines, such as turbine generators.
Large turbine generators are highly reliable machines but they are nevertheless subject to the possibility of occurrence of various types of faults. It is, of course, highly desirable to detect such faults, or other abnormal conditions, at an early or incipient stage so that remedial action can be taken before a complete failure occurs. One such type of fault is an arcing fault between strands, or between adjacent ends of a broken strand, in the high-voltage stator winding conductors of a generator. The stator windings of a large generator are made up of stranded conductors enclosed in relatively heavy high-voltage insulation and suitably connected together, and faults may occur due to breaking of one or more strands in the conductors themselves or the connections, or to local insulation failures between adjacent strands. Such faults cause intermittent or repeated arcing between the strands, or the strand ends involved, and lead to increasing overheating and eventual breakdown of the major ground insulation, with resulting serious or catastrophic electrical failure. Such a failure can cause serious damage to the machine because of the excessive temperatures and arcing or flashovers within the machine, so that such a fault usually requires extensive repairs with an extended shutdown of the machine and heavy expense. Obviously, it would be desirable to detect the occurrence of such a fault in an early or incipient stage, before any serious damage has occurred, so that remedial action can be taken. Heretofore, it has been attempted to detect such conditions as early as possible during the overheating stage by means of temperature detectors of various kinds or, more recently, by detecting the emission of particulate matter from the insulation itself. Such fault detection methods, however, are dependent on the occurrence of abnormal temperatures and, therefore, do not detect the fault at as early a stage as would be desirable.